574 



NA TURE 



lApri/ r;, 1884 



the approaching International C.eodetic Conference at \ 

 \Vashing;on is beginning to claim decision. I 



The Report describes the nature and general procedure 

 of the coast and topographical surveys, with a description 

 of the instriniients employed ; full details of the observa- 

 tions and- their methods of reduction being given. 



Whilst the original leading aim of the Survey, the 

 security of navigation, has been kept in view, other ob- 

 jects incidental to the work of trigonometrical survey, 

 and of the highest scientific interest, have not been lost 

 sight of. 



Hydrographic surveys have been prosecuted in the 

 waters and off the coasts of seventeen States and Terri- 

 tories, and topographic surveys for the exact definition 

 and delineation of shore line have been carried on in 

 clc\'en States and Territories. The triangulations for this 

 work have been advanced in twenty-two .States and Terri- 

 tories, and included the measurement of the base-line in 

 California ; and also, as is well known, the extension of 

 the trans-continental triangulations urged by the late 

 I'rof. Peirce, for connecting the surveys of the Atlantic 

 and Pacific coas'.s. In the interior States the work has 

 included the continuation of the triangulations of Ken- 

 tucky, Tennessee, and other States. 



The incidental work has comprised the carrying of lines 

 of precise "leveling" between points far distant (1125 

 miles) ; the exchange by telegraphic signal of the longi- 

 tudes of important cities ; the usual observations for lati- 

 tude and azimuth, and of the magnetic elements ; the 

 determination of the force of gravity by pendulum experi- 

 ment ; and the study of ocean currents, particularly of 

 the Gulf Stream. 



For the year ending June 1884 the cost for carrying on 

 the work of the U.S. Coast and Geodetic Survey, by which 

 designation this department lias been known since 1878, 

 was estimated at i?573,ooo, and it is gratifying to note that 

 on the other side of the Atlantic the value of active scien- 

 tific inquiry continues to be recognised by the State, pro- 

 vision having been made for further tidal, magnetic, gravity, 

 and other scientific observations. 



In a geodetic survey extending o\'er an area so large as 

 that of the United States the question of the size and 

 figure of the earth becomes of great importance. Al- 

 though, as Prof. Hilgard points out, different opinions are 

 held as to the mode of prosecuting gravity experiments, 

 all geodists agree that widely-distributed pendulum ob- 

 servations will give results valuable to geodesy and 

 geology. It is undoubtedly desirable that opportunity 

 should not be lost of combining the results of pendulum 

 observations taken in different parts of the globe, and we 

 trust that thevaluablependulumworkdone in lndia("Great 

 Trigonometrical Survey," vol. v.), and the discussion at 

 the informal conference on gravity determinations be- 

 tween Col. J. Herschel, R.E., Prof. S. Nevvcomb, and the 

 officers of the Survey Department, which was held at 

 Washington in May 1882, may stimulate the recognition 

 in this country of the necessity of further experiment and 

 inquiry in this direction. Although the conclusions pro- 

 posed by Prof. Newcomb, as amended and adopted by 

 the conference, have been elsewhere discussed, it appears 

 desirable at the present time again to invite attention to 

 them. Generally they are as follows : — 



1. The main object of pendulum research is the deter- 

 mination of the figure of the earth. 



2. A complete geodetic survey should include deter- 

 minations of the intensity of gravity. 



3. A minute gravimetric survey of some limited region 

 is at present of such interest as to justify its execution. 



4. Extended gravimetric linear exploration is desirable. 



5. Each series of such determinations should be made 

 with the same apparatus. 



6. Such determinations ought commonly to be accurate 

 to the i/200,oooth part. 



7. All pendulums should be compared at some central 

 station. 



8. Determinations of absolute gravity will probably 

 prove useful in comparing the yard and the metre, and 

 they should at any rate be made in order to test the 

 constancy of gravity against the constancy of length of a 

 metallic bar. 



9. In the present state of our experience, unchanged 

 pendulums are decidedly to be preferred for ordimry 

 explorations. 



In an appendix (No. 21) is given the reduction, with 

 the employment of modern constants, made by the late 

 Dr. C. R. Powalky at the charge of the Bache Fund of the 

 National Academy of Sciences, of the places of 150 stars 

 observed by La Caille at the Cape of Good Hope and at 

 Paris, between 1749 ^"d 1757. Since all these stars have 

 been re-ob;erved in recent years at Melbourne and at the 

 Cape, the comparisons of La Caille's places with these 

 determinations and with those of Dr. B. A. Gould at 

 Cordoba became of scientific value. 



An account is also given of the measurement of the 

 primary base-line in Yolo county, Sacramento Valley, 

 begun in 1879 with the new compensating base apparatus 

 designed by Assistant C. A. Schott. The measurement 

 was made under the directions of Assistant George David- 

 son, but the discussion of its results does not appear in 

 the present Report 



The measuring bar of the compensating apparatus is of 

 a construction different from other compensating bars, 

 but involves no new mechanical principle. It is com- 

 posed of two rnetals, zinc and steel, so proportioned as to 

 be compensatory for change of temperature, the expansion 

 or contraction of a zinc bar five metres in length 

 being counteracted by the expansion or contraction of 

 the two steel bars between which it is placed. 



The determination of the rate of expansion of the 

 subsidiary steel and zinc bars by which the five-metre 

 standard was verified was done by means of two micro- 

 meter microscropes securely fixed to stone piers placed a 

 metre apart, the metre bar whose rate of expansion was 

 to be determined being compared when at dift'erent tem- 

 peratures with the distance between the two microscopes 

 as determined at a constant temperature by reference to 

 a second standard metre bar. The distance between the 

 microscopes thus becomes a function of the temperature, 

 and in this respect we cannot but think that the method 

 attributed to General Wrede, by which the variable 

 distance between the microscopes becomes unimport- 

 ant, has a decided advantage. 



The active investigations since 1871 as to the dis- 

 tribution of terrestrial magnetism in North America 

 have beome generally known from the reports of Prof. 

 Hilgard, as well as by the publication ot Mr. Schott's 

 paper on the magnetic variation of secular declination. 

 Mr. Schott also now gives an important appendix to 

 the Report on the distribution of the magnetic declina- 

 tion in the United States at the epoch January 1885, 

 together with three isogenic charts in continuation of 

 those issued by the Survey up to the year 1876. The 

 results are also given of the magnetic observations made 

 by Lieut. Very on the north-eastern coast of America, 

 particularly at Labrador, in the remote settlement of Nain 

 (lat. = 56° 33' N., long. 61- 44' W.). 



In the exploration of the Gulf Stream, the facts brought 

 out by the deep sea soundings of Commander J. R. 

 Bartlett during 18S1, with Siemens's admirable electrical 

 deep-sea thermometer, are also referred to ; and the 

 account of the deep-sea soundings taken off the Atlantic 

 coast between 1879 '^nd 18S3 by Lieut. J. E. Pillsbury, in 

 connection with the exploration of the Gulf Stream, and 

 the discussion by Prof. Ferrel on the tides of the Pacific 

 coast are now published. The inquiries of Dr. Thos. 

 Craig as to fluid motion, particularly as to the motion of 



